Modular heated cover

ABSTRACT

The grounded modular heated cover is disclosed with a first pliable outer layer and a second pliable outer layer, wherein the outer layers provide durable protection, an electrical heating element between the first and the second outer layers, the electrical heating element configured to convert electrical energy to heat energy, a heat spreading layer, and a thermal insulation layer positioned above the active electrical heating element. Beneficially, such a device provides radiant heat, weather isolation, temperature insulation, and solar heat absorption efficiently and cost effectively. The modular heated cover quickly and efficiently removes ice, snow, and frost from surfaces, and penetrates soil and other material to thaw the material to a suitable depth. A plurality of modular heated covers can be connected on a single 120 Volt circuit protected by a 20 Amp breaker. The modular heated covers are grounded for safety using the conductive heat spreading layer.

This application is a continuation of U.S. application Ser. No.12/212,529 filed on Sep. 17, 2008 titled A GROUNDED MODULAR HEATEDCOVER, which is a continuation-in-part of U.S. application Ser. No.11/835,641 filed on Aug. 8, 2007 titled GROUNDED MODULAR HEATED COVER,which is a continuation in part of U.S. patent application Ser. No.11/744,163 filed May 3, 2007. This application is also a continuation inpart of co-pending U.S. application Ser. No. 11/422,580 filed on Jun. 6,2006, titled “A RADIANT HEATING APPARATUS” which claims priority to U.S.Provisional Patent Application 60/688,146 filed Jun. 6, 2005, titledLAMINATE HEATING APPARATUS. U.S. application Ser. No. 11/422,580 filedon Jun. 6, 2006, titled “A RADIANT HEATING APPARATUS” is a Continuationin Part of U.S. patent application Ser. No. 11/218,156, filed Sep. 1,2005, now U.S. Pat. No. 7,230,213 issued on Jun. 12, 2007, which claimspriority to: U.S. Provisional Patent Application 60/654,702 filed onFeb. 17, 2005, titled A MODULAR ACTIVELY HEATED THERMAL COVER; U.S.Provisional Patent Application 60/656,060 filed Feb. 23, 2005 titled AMODULAR ACTIVELY HEATED THERMAL COVER; and U.S. Provisional PatentApplication 60/688,146 filed Jun. 6, 2005, titled LAMINATE HEATINGAPPARATUS. U.S. application Ser. No. 11/422,580 filed on Jun. 6, 2006,titled “A RADIANT HEATING APPARATUS” is also a Continuation in Part ofU.S. patent application Ser. No. 11/344,830, filed Feb. 1, 2006 now U.S.Pat. No. 7,183,524 issued on Feb. 27, 2007, which claims priority to:U.S. Provisional Patent Application 60/654,702 filed on Feb. 17, 2005,titled A MODULAR ACTIVELY HEATED THERMAL COVER; U.S. Provisional PatentApplication 60/656,060 filed Feb. 23, 2005 titled A MODULAR ACTIVELYHEATED THERMAL COVER; and U.S. Provisional Patent Application 60/688,146filed Jun. 6, 2005, titled LAMINATE HEATING APPARATUS.

BACKGROUND

Ice, snow and, frost create problems in many areas of construction. Forexample, when concrete is poured the ground must be thawed and free ofsnow and frost. In agriculture, planters often plant seeds, bulbs, andthe like before the last freeze of the year. In such examples, it isnecessary to keep the concrete, soil, and other surfaces free of ice,snow, and frost. In addition, curing concrete requires that the ground,ambient air, and newly poured concrete maintain a temperature betweenabout 50 degrees and about 90 degrees. In industrial applications,outdoor pipes and conduits often require heating or insulation to avoiddamage caused by freezing. In residential applications, it is beneficialto keep driveways and walkways clear of snow and ice.

Standard methods for removing and preventing ice, snow, and frostinclude blowing hot air or water on the surfaces to be thawed, runningelectric heat trace along surfaces, and/or laying tubing or hosescarrying heated glycol or other fluids along a surface. Unfortunately,such methods are often expensive, time consuming, inefficient, andotherwise problematic.

Ice buildup is particularly problematic in the construction industry.For example, ice and snow may limit the ability to pour concrete, layroofing material, and the like. In these outdoor constructionsituations, time and money are frequently lost to delays caused by snowand ice. If delay is unacceptable, the cost to work around the situationmay be unreasonable. For example, to pour concrete, the ground must bethawed to a reasonable depth to allow the concrete to adhere to theground and cure properly. Typically, in order to pour concrete infreezing conditions, earth must be removed to a predetermined depth andreplaced with gravel. This process is costly in material and labor.

In addition, it is important to properly cure the concrete for strengthonce it has been poured. Typically the concrete must cure for aboutseven days at a temperature within the range of 50 degrees Fahrenheit to90 degrees Fahrenheit, with 70 degrees Fahrenheit as the optimumtemperature. If concrete cures in temperatures below 50 degreesFahrenheit, the strength and durability of the concrete is greatlyreduced. In an outdoor environment where freezing temperatures exist ormay exist, it is difficult to maintain adequate curing temperatures.

In roofing and other outdoor construction trades, it may be similarlyimportant to keep work surfaces free of snow, ice, and frost.Additionally, it may be important to maintain specific temperatures forsetting, curing, laying, and pouring various construction productsincluding tile, masonry, or the like.

Although the need for a solution to these problems is particularly greatin outdoor construction trades, a solution may be similarly beneficialin various residential, industrial, manufacturing, maintenance, andservice fields. For example, a residence or place of business with anoutdoor canopy, car port, or the like may require such a solution tokeep the canopy free of snow and ice in order to prevent damage from theweight of accumulated precipitation or frost. Conventional solutions forkeeping driveways, overhangs, and the like clear of snow typicallyrequire permanent fixtures that are both costly to install and operate,or small portable devices that do not cover sufficient surface area.

While some solutions are available for construction industries to thawground, keep ground thawed, and cure concrete, these solutions arelarge, expensive to operate and own, time consuming to setup and takedown, and complicated. Conventional solutions employ heated air, oil, orfluid delivered to a thawing site by hosing. Typically, the hosing isthen covered by a cover such as a tarp or enclosure. Laying andarranging the hosing and cover can be time consuming. Furthermore,heating and circulating the fluid requires significant energy in theform of heaters, pumps, and/or generators.

Currently, few conventional solutions use electricity to produce andconduct heat. Traditionally, this was due to limited circuit designs.Traditional solutions were unable to produce sufficient heat over asufficient surface area to be practical. The traditional solutions thatdid exist required special electrical circuits with higher voltages andprotected by higher-rated breakers. These special electrical circuitsare often unavailable at a construction site. Thus, using standardcircuits, conventional solutions are unable to produce sufficient heatover a sufficiently large surface area to be practical. Typically, 143BTUs are required to melt a pound of ice. Conventional electricallypowered solutions are incapable of providing 143 BTUs over asufficiently large enough area for practical use in the constructionindustry. Consequently, the construction industry has turned to bulky,expensive, time consuming heated fluid solutions.

A further complication results from the relatively large current drawnthrough a modular heated cover, as described above. In order to useelectricity to provide a solution, significant amounts of current areneeded to provide the necessary heat. This high current may pose asafety risk to those working with or around the device. A brokenelectrical component which conducts electricity may pose a significantrisk to a person who comes into contact with the broken component. Atraditional solution to provide grounding would be to add a layer ofconductive material to the cover and connect a grounding lead to thefoil layer. However, adding another layer requires additional rawmaterial and additional work in the manufacturing process, increasingthe material costs and the cost of manufacturing the device. Inaddition, adding another layer increases the weight of the cover and maydecrease its flexibility. Since the cover should ideally be mobile andflexible, adding a grounding layer lessens the effectiveness of thecover.

What is needed is a modular heated cover that operates using electricityfrom standard job site power supplies, is cost effective, portable,reusable, and modular to provide heated coverage for variable sizesurfaces efficiently and cost effectively. For example, the modularheated cover may comprise a pliable material that can be rolled orfolded and transported easily. Furthermore, the modular heated coverwould be configured such that two or more modular heated covers caneasily be joined to accommodate various surface sizes. Beneficially,such a device would provide directed radiant heat, modularity, weatherisolation, temperature insulation, and solar heat absorption. Themodular heated cover would maintain a suitable temperature for exposedconcrete to cure properly and quickly and efficiently remove ice, snow,and frost from surfaces, as well as penetrate soil and other material tothaw the material to a suitable depth for concrete pours and otherconstruction projects. In addition, the modular heated covers should beconfigured such that they are less likely to result in harm to anindividual working with the covers in the event of an electrical failurein one or more covers. Ideally, the modular heated covers should begrounded in a manner that does not decrease flexibility, increaseweight, or require the addition of new layers to the cover.

SUMMARY

The present invention has been developed in response to the presentstate of the art, and in particular, in response to the problems andneeds in the art that have not yet been fully solved by currentlyavailable ground covers. Accordingly, the present invention has beendeveloped to provide a grounded modular heated cover and associatedsystem that overcome many or all of the above-discussed shortcomings inthe art.

A grounded modular heated cover is presented which comprises a pliableelectrical heating element configured to convert electrical energy toheat energy. The pliable electrical heating element comprises aresistive element for converting electrical current to heat energy. Thepliable electrical heating element further comprises a substantiallyplanar heat-spreading element comprising an electrically-conductivematerial comprising carbon. The heat-spreading element is situatedproximate to the resistive element, and an electrically insulatingelement separates the resistive element from the heat-spreading elementsuch that the resistive element is not in electric communication withthe heat-spreading element.

The grounded modular heated cover further comprises a pliable outerlayer configured to circumscribe the pliable electrical heating elementand provide durable protection in an outdoor environment and a receivingpower coupling configured to couple to a power source, the receivingpower coupling further comprising a hot prong and a neutral prong, thehot prong and neutral prong electrically connected to the resistiveelement, and a grounding prong, the grounding prong electricallyconnected to the heat-spreading element.

In certain embodiments, the grounded modular heated cover furthercomprises a female electric power coupling configured to optionallycouple a first grounded modular heated cover to a second groundedmodular heated cover by receiving the receiving power coupling of thesecond grounded modular heated cover, the female electric power couplingcomprising a hot prong coupler and a neutral prong coupler connected tothe pliable electrical heating element of the first grounded modularheated cover and a grounding prong coupler electrically connected to theheat-spreading element of the first grounded modular heated cover.

The grounded modular heated cover may also have the receiving powercoupling configured to be connected to a 120 Volt power source, and asecond receiving power coupling configured to be connected to a 240 Voltpower source, the second receiving power coupling further comprising ahot prong and a neutral prong electrically connected to the resistiveelement and a grounding prong electrically connected to theheat-spreading element.

In certain embodiments the grounded modular heated cover furthercomprises a grounding layer, which grounding layer is electricallyinsulated from the resistive element and situated such that theresistive element is situated between the grounding layer and theheat-spreading element, the grounding layer proximate to the resistiveelement and electrically connected to the grounding prong of thereceiving power coupling.

The grounded modular heated cover may also comprise a grounding sheath,the grounding sheath encompassing the resistive element and furtherconfigured to be electrically connected to the grounding prong of thereceiving power coupling.

The grounding prong may further comprise a connection blade, and theconnection blade may be electrically connected to the heat-spreadingelement such that an electric connection is made along the plane of theheat-spreading element. In certain embodiments, the heat spreadingelement is approximately three feet wide and twenty-three feet long andbetween approximately 1 thousandths of an inch thick and about 40thousandths of an inch thick.

Also disclosed is a system for heating a surface, which system comprisesa power source configured to supply an electrical current on a 120 voltelectric circuit having a breaker rated up to about 20 Amps, the powersource further comprising a ground connection. The system also comprisesone or more grounded modular heated covers which comprise an outer layerproviding durable protection for inner layers which comprise anelectrical heating element configured to convert electrical energy toheat energy.

The inner layers further comprise a planar heat spreading elementcomprising an electrically-conductive carbon allotrope inelectrically-insulated contact with the electrical heating element. Theheat-spreading element is configured to distribute the heat energygenerated by the electrical heating element.

The surface area of the modular heated cover is between approximatelyten square feet and approximately 253 square feet. The modular heatedcover also comprises a receiving electrical power plug comprising a hotprong and a neutral prong electrically connected to the electricalheating element such that electrical energy is obtained from the powersource. The receiving electrical power plug further comprises agrounding prong electrically connected to the heat-spreading element. Inaddition, the modular heated cover comprises a connecting electricalpower plug for conveying electrical energy from a first modular heatedcover to a second modular heated cover, the connecting electric powerplug comprising a hot prong and a neutral prong connected to the pliableelectrical heating element and a grounding prong electrically connectedto the heat-spreading element.

The system may further comprise a plurality of connecting electric powerplugs and receiving electric power plugs disposed about the perimeter ofthe thermal cover for coupling multiple modular thermal covers. Further,a plurality of grounded modular heated covers may be electricallyconnected with the receiving electrical power plug of a second groundedmodular heated cover coupled to the connecting electrical power plug ofthe first grounded modular heated cover, the electrical connection suchthat an electrical ground connection is established from each of theplurality of grounded modular heat covers to the ground connection ofthe power source.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating one embodiment of a systemfor implementing a modular heated cover;

FIG. 2 is a schematic diagram illustrating one embodiment of a modularheated cover;

FIG. 3 is a schematic cross-sectional diagram illustrating oneembodiment of a modular heated cover;

FIG. 4 is a schematic cross-sectional diagram illustrating oneembodiment of an air isolation flap;

FIG. 5 is a schematic block diagram illustrating one embodiment of atemperature control module;

FIG. 6 is a schematic block diagram illustrating one embodiment of anapparatus for providing versatile power connectivity and thermal output;

FIG. 7 is a schematic block diagram illustrating one embodiment of amodular heated cover;

FIG. 8 is a schematic block diagram illustrating one embodiment of amodular heated cover with integrated electrical heating elements;

FIG. 9 is a schematic cross-sectional diagram illustrating oneconfiguration for grounding a modular heated cover;

FIG. 10 is a schematic block diagram illustrating an alternativeconfiguration comprising a grounding layer for grounding a modular heatcover;

FIG. 11 is a schematic block diagram illustrating an exemplaryembodiment of a grounding connection for a system comprising a pluralityof modular heated covers; and

FIG. 12 is a schematic block diagram illustrating an alternativeconfiguration comprising a grounding sheath for grounding a modular heatcover.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

Furthermore, the described features, structures, or characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details areprovided, such as examples of materials, layers, connectors, conductors,insulators, and the like, to provide a thorough understanding ofembodiments of the invention. One skilled in the relevant art willrecognize, however, that the invention may be practiced without one ormore of the specific details, or with other methods, components,materials, and so forth. In other instances, well-known structures,materials, or operations are not shown or described in detail to avoidobscuring aspects of the invention.

FIG. 1 illustrates one embodiment of a system 100 for implementing agrounded modular heated cover. In one embodiment, the system 100includes a surface 102 to be heated, one or more modular heated covers104, one or more electrical coupling connections 106, a power extensioncord 108, and an electrical power source 110.

In various embodiments, the surface to be heated 102 may be planer,curved, or of various other geometric forms. Additionally, the surfaceto be heated 102 may be vertically oriented, horizontally oriented, ororiented at an angle. In one embodiment, the surface to be heated 102 isconcrete. For example, the surface 102 may include a planar concretepad. Alternatively, the surface may be a cylindrical concrete pillarpoured in a vertically oriented cylindrical concrete form. In suchembodiments, the thermal cover 104 may melt frost, ice and snow on theconcrete and prevent formation of ice, frost and snow on the surface ofthe concrete and thermal cover 104.

In another alternative embodiment, the surface 102 may be ground soil ofvarious compositions. In certain circumstances, it may be necessary toheat a ground surface 102 to thaw frozen soil and melt frost and snow,or prevent freezing of soil and formation of frost and snow on thesurface of the soil and thermal cover 104. It may be necessary to thawfrozen soil to prepare for pouring new concrete. One of ordinary skillin the art of concrete will recognize the depth of thaw required forpouring concrete and the temperatures required for curing concrete.Alternatively, the surface 102 may comprise poured concrete that hasbeen finished and is beginning the curing process.

In one embodiment, one or more modular heated covers 104 are placed onthe surface 102 to thaw or prevent freezing of the surface 102. Aplurality of thermal covers 104 may be connected by electrical couplingconnections 106 to provide heat to a larger area of the surface 102. Inone embodiment, the modular heated covers 104 may include a physicalconnecting means, an electrical connector, one or more insulationlayers, and an active electrical heating element. The electrical heatingelements of the thermal covers 104 may be connected in a seriesconfiguration. Alternatively, the electrical heating elements of thethermal covers 104 may be connected in a parallel configuration.Detailed embodiments of modular heated covers 104 are discussed furtherwith relation to FIG. 2 through FIG. 4.

In certain embodiments, the electrical power source 110 may be a poweroutlet connected to a 120V or 240 V AC power line. Alternatively, thepower source 110 may be an electricity generator. In certainembodiments, the 120V power line may supply a range of current betweenabout 15 A and about 50 A of electrical current to the thermal cover104. Alternative embodiments of the power source 110 may include a 240VAC power line. The 240V power line may supply a range of current betweenabout 30 A and about 70 A of current to the thermal cover 104. Variousother embodiments may include supply of three phase power, DirectCurrent (DC) power, 110 V or 220 V power, or other power supplyconfigurations based on available power, geographic location, and thelike. Ideally, the power source 110 comprises a standard three-prongconnection and provides an electrical ground for devices coupled to thepower source 110.

In one embodiment, a power extension cord 108 may be used to create anelectrical connection between a modular heated cover 104, and anelectrical power source 110. In one embodiment, the extended electricalcoupler 108 is a standard extension cord. Alternatively, the extendedelectrical coupler 108 may include a heavy duty conductor such as 4gauge copper and the required electrical connector configuration toconnect to high power outlets. Power extension cords 108 may be used toconnect the power source 110 to the thermal covers 104, or to connectone thermal cover 104 to another thermal cover 104. In such embodiments,the power extension cords 108 are configured to conduct sufficientelectrical current to power the electrical heating element of themodular heated covers 104. One of ordinary skill in the art of powerengineering will understand the conductor gauge requirements based onthe electric current required to power the thermal cover 104.

FIG. 2 illustrates one embodiment of a modular heated cover 200. In oneembodiment, the cover 200 includes a multilayered cover 202. Themultilayered cover 202 may include a flap 204. Additionally, the cover200 may be coupled to an electrical heating element. In one embodiment,the electrical heating element comprises a resistive element 208 and aheat spreading element 210. The electrical heating element may furthercomprise an electrical insulating element described in greater detailbelow. The cover 200 may additionally include one or more fasteners 206,one or more electric power connections 212, one or more electric powercouplings 214, and an electrical connection 216 between the connections212 and the couplings 214. In certain embodiments the thermal cover 200may additionally include a GFI device 218 and one or more creases 220.

The multilayered cover 202 may comprise a textile fabric. The textilefabric may include natural or synthetic products. For example, themultilayered cover 202 may comprise burlap, canvas, or cotton. Inanother example, the multilayered cover 202 may comprise nylon, vinyl,or other synthetic textile material. For example, the multilayered cover202 may comprise a thin sheet of plastic, metal foil, polystyrene, orthe like. Further embodiments of the multilayered cover 202 arediscussed below with regard to FIG. 3.

In one embodiment, the flap 204 may overlap another thermal cover 200.The flap 204 may provide isolation of air trapped beneath the thermalcover 200. Isolation of the air trapped beneath the thermal cover 200prevents heat loss due to air circulation. Additionally, the flap 204may include one or more fasteners 206 for hanging, securing, orconnecting the thermal cover 200. In one embodiment, fasteners 206 maybe attached to the corners of the cover 200. Additionally, fasteners 206may be distributed about the perimeter of the cover 200. In oneembodiment, the fastener 206 is Velcro™. For example, the flap mayinclude a hook fabric on one side and a loop fabric on the other side.In another alternative embodiment, the fastener 206 may include snaps,zippers, adhesives, and the like.

In another embodiment, the flap 204 may be weighted to hold the flap 204into position to retain air. For example, the flap 204 may comprise apocket that may be filled with a weight material, such as sand, snow,soil, water, or gravel. In certain embodiments, the pocket may be filledby a user when the modular heated cover 200 is in use, and emptied forstorage and transport.

In one embodiment, the electrical heating element comprises anelectro-thermal coupling material or resistive element 208. For example,the resistive element 208 may be a copper conductor. The copperconductor may convert electrical energy to heat energy, and transfer theheat energy to the surrounding environment. Alternatively, the resistiveelement 208 may comprise another conductor capable of convertingelectrical energy to heat energy. One skilled in the art ofelectro-thermal energy conversion will recognize additional materialsuitable for forming the resistive element 208. Additionally, theresistive element 208 may include one or more layers for electricalinsulation, temperature regulation, and ruggedization. In oneembodiment, the resistive element 208 may include two conductorsconnected at one end to create a closed circuit that can be connected toa power source comprising a hot and a neutral connection.

Additionally, the electrical heating element may comprise a heatspreading element 210. In general terms, the heat spreading element 210is a layer or material capable of drawing heat from the resistiveelement 208 and distributing the heat energy away from the resistiveelement 208. Specifically, the heat spreading element 210 may comprise ametallic foil, graphite, carbon composites, a composite material, orother substantially planar material. Preferably, the heat spreadingelement 210 comprises a material that is thermally anisotropic such thatheat is more efficiently transferred in one plane. The thermallyanisotropic material may distribute the heat energy more evenly and moreefficiently. The heat spreading element 210, in one embodiment,conducts, transfers, and evenly distributes heat energy from theresistive element 208 to a large surface area.

The heat-spreading element 220 in one embodiment is anelectrically-conductive material comprising carbon. Graphite is oneexample of an electrically-conductive material comprising carbon.However, other suitable materials may include carbon-based powders,carbon fiber structures, or carbon composites. Those of skill in the artwill recognize that material comprising carbon may further compriseother elements, whether they represent impurities or additives toprovide the material with particular additional features. Materialscomprising carbon may be suitable so long as they have sufficientthermal conductivity to act as a heat-spreading element 210. In oneembodiment, the material comprising carbon comprises sufficientelectrical conductivity to act as a ground connection. Theheat-spreading element 220 may further comprise a carbon derivative, ora carbon allotrope.

One example of a material suitable for a heat spreading layer 210 is agraphite-epoxy composite. The in-plane thermal conductivity of agraphite-epoxy composite material is approximately 370 watts per meterper Kelvin, while the out of plane thermal conductivity of the samematerial is 6.5 watts per meter per Kelvin. The thermal anisotropy ofthe graphite/epoxy composite material is then 57, meaning that heat isconducted 57 times more readily in the plane of the material thanthrough the thickness of the material. This thermal anisotropy allowsthe heat to be readily spread out from the surface which in turn allowsfor more heat to be drawn out of the resistive elements 208.

Another such material suitable for forming the heat spreading layer 210is GRAFOIL® available from Graftech Inc. located in Lakewood, Ohio.GRAFOIL® is a graphite sheet product made by taking particulate graphiteflake and processing it through an intercalculation process usingmineral acids. The flake is heated to volatilize the acids and expandthe flake to many times its original size. The result is a sheetmaterial that typically exceeds 98% carbon by weight. The sheets areflexible, lightweight, compressible resilient, chemically inert, firesafe, and stable under load and temperature. The sheet materialtypically includes one or more laminate sheets that provide structuralintegrity for the graphite sheet.

Due to its crystalline structure, GRAFOIL® is significantly morethermally conductive in the plane of the sheet than through the plane ofthe sheet. This superior thermal conductivity in the plane of the sheetallows temperatures to quickly reach equilibrium across the breadth ofthe sheet.

Typically, the GRAFOIL® will have no binder, resulting in a very lowdensity, making the heated cover relatively light while maintaining thedesired thermal conductivity properties. For example, the standarddensity of GRAFOIL® is about 1.12 g/ml. It has been shown that threestacked sheets of 0.030″ thick GRAFOIL® C have similar thermal couplingperformance to a 0.035″ sheet of cold rolled steel, while weighing about60% less than the cold rolled steel sheet.

Another product produced by GrafTech Inc. that is suitable for use as aheat spreading element 210 is eGraf® SpreaderShield™. The thermalconductivity of the SpreaderShield™ products ranges from 260 to 500watts per meter per Kelvin within the plane of the material, and thatthe out of plane (through thickness) thermal conductivity ranges from6.2 down to 2.7 watts per meter per Kelvin. The thermal anisotropy ofthe material ranges from 42 to 163. Consequently, a thermallyanisotropic planar heat spreading element 210 serves as a conduit forthe heat within the plane of the heat spreading element 210, and quicklydistributes the heat more evenly over a greater surface area than afoil. The efficient planar heat spreading ability of the planar heatspreading element 210 also provides for a higher electrical efficiency,which facilitates the use of conventional power supply voltages such as120 volts on circuits protected by 20 Amp breakers, instead of lessaccessible higher voltage power supplies.

Preferably, the heat spreading element 210 is a planar thermalconductor. In certain embodiments, the heat spreading layer 210 isformed in strips along the length of the resistive element 208. Inalternative embodiments, the heat spreading element 210 may comprise acontiguous layer. In certain embodiments, the heat spreading layer 210may cover substantially the full surface area covered by the thermalcover 200 for even heat distribution across the full area of the thermalcover 200.

In certain embodiments, the resistive element 208 is in direct contactwith the heat spreading element 210 to ensure efficient thermo-coupling.Alternatively, the heat spreading element 210 and the resistive element208 are integrally formed. For example, the heat spreading element 210may be formed or molded around the resistive element 208. Alternatively,the resistive element 208 and the heat spreading element 210 may beadhesively coupled.

In one embodiment, the thermal cover 200 includes means, such aselectrical coupling connections 106, for electric power transfer fromone thermal cover 200 to another in a modular chain. For example, thethermal cover 200 may include an electric connection 212 and an electriccoupling 214. In one embodiment, the electric connection 212 and theelectric coupling 214 may include an electric plug 212 and an electricsocket 214, and are configured according to standard requirementsaccording to the power level to be transferred. For example, theelectric plug 212 and the electric socket 214 may be standard two prongconnectors for low power applications. Alternatively, the plug 212 andsocket 214 may be a three prong grounded configuration, or a specializedprong configuration for higher power transfer.

In one embodiment, the electrical connection 216 is an insulated wireconductor for transferring power to the next thermal cover 200 in amodular chain. The electrical connection 216 may be connected to theelectric plug 212 and the electric socket 214 for a power transferinterface. In one embodiment, the electrical connection 216 isconfigured to create a parallel chain of active electrical heatingelements 210. Alternatively, the electrical connection 216 is configuredto create a series configuration of active electrical heating elements210. In an alternative embodiment, the resistive element 212 mayadditionally provide the electrical connection 216 without requiring aseparate conductor. In certain embodiments, the electrical connection216 may be configured to provide electrical power to a plurality ofelectrical power couplings 214 positioned at distributed points on thethermal cover 200 for convenience in coupling multiple modular thermalcovers 200. For example, a second thermal cover 200 may be connected toa first thermal cover 200 by corresponding power couplings 214 tofacilitate positioning of the thermal covers end to end, side by side,in a staggered configuration, or the like.

Additionally, the thermal cover 200 may include a Ground FaultInterrupter (GFI) or Ground Fault Circuit Interrupter (GFCI) safetydevice 218. The GFI device 218 may be coupled to the power connection212. In certain embodiments, the GFI device 218 may be connected to theresistive element 208 and interrupt the circuit created by the resistiveelement 208. The GFI device 218 may be provided to protect the thermalcover 200 from damage from spikes in electric current delivered by thepower source 110.

In certain additional embodiments, the thermal cover 200 may include oneor more creases 220 to facilitate folding the thermal cover 200. Thecreases 220 may be oriented across the width or length of the thermalcover 200. In one embodiment, the crease 220 is formed by heat welding afirst outer layer to a second outer layer. Preferably, the thermal cover200 comprises pliable material, however the creases 220 may facilitatefolding a plurality of layers of the thermal cover 200.

In one embodiment, the thermal cover 200 may be twelve feet bytwenty-five feet in dimension. In another embodiment, the thermal cover200 may be six feet by twenty-five feet. In a more preferred embodiment,the thermal cover 200 is eleven feet by twenty three feet.Alternatively, the thermal cover 200 may be two to four feet by fiftyfeet to provide thermal protection to the top of concrete forms.Additional alternative dimensional embodiments may exist. Consequently,the thermal cover 200 in different size configurations covers betweenabout one square foot up to about two-hundred and fifty-three squarefeet. Preferred embodiments may include sizes for the thermal cover 200of between ten square feet and two hundred and fifty-three square feet.

Beneficially, a two-hundred and fifty-three square foot area is coveredand kept at optimal concrete curing temperatures or at optimal heatingtemperatures for thawing froze or cold soil. Advantageously, the highsquare footage can be heated using a single thermal cover 200 connectedto a single 120 volt circuit. Preferably, the 120 volt circuit isprotected by up to about a 20 Amp breaker. In addition, with the firstthermal cover 200 connected to the power source 110 a second thermalcover 200 can be safely connected to the first thermal cover 200 withouttripping the breaker.

Consequently, the present invention allows up to two or more thermalcovers 200 to be modularly connected such that about five hundred andsix square feet are covered and heated using the present invention.Advantageously, the five hundred and six square feet are heated using asingle 120 Volt circuit protected by up to a 20 Amp breaker. Tests ofcertain embodiments of the present invention have been conducted inwhich two thermal covers 200 were modularly connected to cover aboutfive hundred and six square feet. Those of skill in the art willrecognize that more than two thermal covers may be connected on a single120 Volt circuit with up to a 20 Amp breaker if the watts used per footis lowered.

FIG. 3 illustrates one embodiment of a multilayer modular heated cover300. In one embodiment, the thermal cover 300 includes a first outerlayer 302, a thermal insulation layer 304, a resistive element 208, aheat spreading element 210, and a second outer layer 306. In oneembodiment, the layers of the thermal cover 300 comprise fire retardantmaterial. In one embodiment, the materials used in the various layers ofthe thermal cover 300 are selected for high durability in an outdoorenvironment, light weight, fire retardant, sun and water rot resistantcharacteristics, water resistant characteristics, pliability, and thelike. For example, the thermal cover 300 may comprise material suitablefor one man to fold, carry, and spread the thermal cover 300 in a wet,rugged, and cold environment. Therefore, the material is preferablylightweight, durable, water resistant, fire retardant, and the like.Additionally, the material may be selected based on cost effectiveness.

In one embodiment, the first outer layer 302 may be positioned on thetop of the thermal cover 300 and the second outer layer 306 may bepositioned on the bottom of the thermal cover 300. In certainembodiments, the first outer layer 302 and the second outer layer 306may comprise the same or similar material. Alternatively, the firstouter layer 302 and the second outer layer 306 may comprise differentmaterials, each material possessing properties beneficial to thespecified surface environment.

For example, the first outer layer 302 may comprise a material that isresistant to sun rot such as such as polyester, plastic, and the like.The bottom layer 306 may comprise material that is resistant to mildew,mold, and water rot such as nylon. The outer layers 302, 306 maycomprise a highly durable material. The material may be textile orsheet, and natural or synthetic. For example, the outer layers 302, 306may comprise a nylon textile. Additionally, the outer layers 302, 306may be coated with a water resistant or waterproofing coating. Forexample, a polyurethane coating may be applied to the outer surfaces ofthe outer layers 302, 310. Additionally, the top and bottom outer layers302, 306 may be colored, or coated with a colored coating such as paint.In one embodiment, the color may be selected based on heat reflective orheat absorptive properties. For example, the top layer 302 may becolored black for maximum solar heat absorption. The bottom layer 302may be colored grey for a high heat transfer rate or to maximize heatretention beneath the cover.

In another embodiment, the modular heated cover 300 may include a singleouter layer 306. The single outer layer 306 may be disposed on thebottom of the modular heated cover 300 and provide durable protection inan outdoor environment to other components of the modular heated cover300. In certain embodiments, the modular heated cover 300 may include asingle outer layer 307 (comprised of both 302 and 306) configured towrap around the components of the modular heated cover 300. The singleouter layer 307 may form a water tight envelope to protect the modularheated cover 300.

In one embodiment, the thermal insulation layer 304 provides thermalinsulation to retain heat generated by the resistive element 208 beneaththe thermal cover 300. In one embodiment, the thermal insulation layer304 is a sheet of polystyrene. Alternatively, the insulation layer mayinclude cotton batting, Gore-Tex®, fiberglass, or other insulationmaterial. In certain embodiments, the thermal insulation layer 304 mayallow a portion of the heat generated by the resistive element 208 toescape the top of the thermal cover 300 to prevent ice and snowaccumulation on top of the thermal cover 300. For example, the thermalinsulation layer 304 may include a plurality of vents to transfer heatto the top layer 302. In certain embodiments, the thermal insulationlayer 304 may be integrated with either the first outer layer 302 or thesecond outer layer 306. For example, the first outer layer 302 maycomprise an insulation fill or batting positioned between two films ofnylon.

In certain embodiments, the modular heated cover 300 may be constructedwith no thermal insulation layer 304 or with a minimal or nominalthermal insulation layer 304. In these embodiments, the modular heatedcover 300 may be used alone, or in conjunction with a separateinsulation layer. In embodiments without thermal insulation layers 304,the modular heated cover 300 may have reduced weight and bulk, andseparate insulation may be added to the top of the modular heated cover300 to match the needs of the surrounding environment. Examples ofseparate insulation layers include blankets made from cotton batting,fiberglass, straw, conventional passive concrete curing blankets, or thelike.

In one embodiment, the heat spreading element 210 is placed in directcontact with the resistive element 208. The heat spreading element 210may conduct heat away from the resistive element 208 and spread the heatfor a more even distribution of heat. The heat spreading element 210 maycomprise any heat conductive material. For example, the heat spreadingelement 210 may comprise metal foil, wire mesh, and the like. In oneembodiment, the resistive element 208 may be wrapped in metal foil. Theresistive element 208 may be made from metal such as copper or otherheat conductive material such as graphite. Alternatively, the conductivelayer may comprise a heat conducting liquid such as water, oil, greaseor the like.

Alternatively, the heat spreading element 210 is placed proximate to theresistive element 208 such that the two are not in electrical contact,but sufficiently close to allow for efficient thermal transfer. Incertain embodiments, this entails the resistive element 208 being within¼ inch of the heat spreading element 210 or closer.

FIG. 4 illustrates a cross-sectional diagram of one embodiment of an airisolation flap 400. In one embodiment, the air isolation flap 400includes a portion of a covering sheet 402, a weight 404, a bottomconnecting means 406, and a top connecting means 408. In one embodiment,the air isolation flap 400 may extend six inches from the edges of thethermal covering 300. In one embodiment, the air isolation flap 400 mayadditionally include heavy duty riveted, or tubular edges (not shown)for durability and added air isolation. The covering sheet 402 maycomprise a joined portion of the first outer cover 302 and second outercover 306 that extends around the perimeter of the cover 200 and doesnot include any intervening layers such as heat spreading layer 210 orthermal insulation layer 304.

In one embodiment, the weight 404 is lead, sand, or other weightedmaterial integrated into the air isolation flap 400. Alternatively, theweight may be rock, dirt, or other heavy material placed on the airisolation flap 400 by a user of the thermal cover 200.

In one embodiment, the bottom connecting means 406 and the topconnecting means 408 may substantially provide air and water isolation.In one embodiment, the top and bottom connecting means 408, 406 mayinclude weather stripping, adhesive fabric, Velcro, or the like.

FIG. 5 illustrates one embodiment of a modular temperature control unit500. In one embodiment, the temperature control unit may include ahousing 502, control logic 506, a DC power supply 508 connected to an ACpower source 504, an AC power supply for the thermal cover 200, a userinterface 510 with an adjustable user control 512, and a temperaturesensor 514.

In one embodiment, the control logic 506 may include a network ofamplifiers, transistors, resistors, capacitors, inductors, or the likeconfigured to automatically adjust the power output of the AC powersupply 516, thereby controlling the heat energy output of the resistiveelement 208. In another embodiment, the control logic 206 may include anintegrated circuit (IC) chip package specifically for feedback controlof temperature. In various embodiments, the control logic 506 mayrequire a 3V-25V DC power supply 508 for operation of the control logiccomponents.

In one embodiment, the user interface 510 comprises an adjustablepotentiometer. Additionally, the user interface 510 may comprise anadjustable user control 512 to allow a user to manually adjust thedesired power output. In certain embodiments, the user control mayinclude a dial or knob. Additionally, the user control 512 may belabeled to provide the user with power level or temperature levelinformation.

In one embodiment, the temperature sensor 514 is integrated in thethermal cover 200 to provide variable feedback signals determined by thetemperature of the thermal cover 200. For example, in one embodiment,the control logic 506 may include calibration logic to calibrate thesignal level from the temperature sensor 514 with a usable feedbackvoltage.

FIG. 6 illustrates one embodiment of an apparatus 600 for providingversatile power connectivity and thermal output. In one embodiment, theapparatus 600 includes a first electrical plug 602 configured for 120Vpower, a second electrical plug 604 configured for 240V power, adirectional power diode 606, a first active electrical heating element608, and a second active electrical heating element 610.

In one embodiment, the first electrical heating element 608 is poweredwhen the 120V plug 602 is connected, but the second electrical heatingelement 610 is isolated by the directional power diode 606. In anadditional embodiment, the first electrical heating element 608, and thesecond electrical heating element 610 are powered simultaneously. Inthis embodiment, the first electrical heating element 608 and the secondelectrical heating element 610 are coupled by the directional powerdiode 606.

In one embodiment, the directional power diode 606 is specified tooperate at 240V and up to 70 A. The directional power diode 606 allowselectric current to flow from the 240V line to the first electricalheating element 608, but stops electric current flow in the reversedirection. In another embodiment, the directional power diode 606 may bereplaced by a power transistor configured to switch on when currentflows from the 240V line and switch off when current flows from the 120Vline.

In one embodiment, the safety ground lines from the 120V connector 602and the 240V connector 604 are connected to thermal cover 200 atconnection point 612. In one embodiment, the safety ground 612 isconnected to the heat spreading element 210. Alternatively, the safetyground 612 is connected to the outer layers 302, 310. In anotheralternative embodiment, the safety ground 612 may be connected to eachlayer of the thermal cover 200.

Beneficially, the apparatus 600 provides high versatility for powerconnections, provides variable heat intensity levels, and the like. Forexample, the first active electrical heating element 608 and the secondactive electrical heating element 610 may be configured within thethermal cover 200 at a spacing of four inches. In one embodiment, thefirst active electrical heating element 608 and the second activeelectrical heating element 610 connect to a hot and a neutral powerline. The electrical heating elements may be positioned within thethermal cover 200 in a serpentine configuration, an interlocking fingerconfiguration, a coil configuration, or the like. When the 120V plug 602is connected, only the first active electrical heating element 608 ispowered. When the 240V plug 604 is connected, both the first activeelectrical heating element 608 and the second active electrical heatingelement 610 are powered. Therefore, the resulting effective spacing ofthe electrical heating elements is only four inches.

The powered lines of both the 120V plug 602 and the 240V plug 604 may beconnected to a directional power diode to isolate the power providedfrom the other plug. Alternatively, a power transistor, mechanicalswitch, or the like may be used in the place of the directional powerdiode to provide power isolation to the plugs. In another embodiment,the both the 120V plug 602, and the 240V plug 604 may include waterproofcaps (not shown). In one embodiment, the caps (not shown) may include apower terminating device for safety.

FIG. 7 illustrates one embodiment of a modular heated cover 700. In oneembodiment, the thermal cover 700 includes one or more 120V plugconnectors 702, one or more 240V plug connectors 704, one or more 120Vreceptacle connectors 706, and one or more 240V receptacle connectors708. Additionally, the thermal cover 700 may include one or more powerbus connections 710 for a 120V power connection, and one or more powerbus connections 712 for a 240V power connection.

In one embodiment, the thermal cover 700 may additionally include apower connection 714 between the 120V power line, and one 120V phase ofthe 240V power line. In certain embodiments, the connection 714 providespower to a first active electrical heating element 716 when the 240Vpower connector 704 is plugged in. In one embodiment, the 240V powerconnector 704 may additionally provide power to a second activeelectrical heating element 718. The 120V power connector 702 may providepower to the first active electrical heating element 716, but not thesecond active electrical heating element 718. For example, if the 120Vpower connector 702 is connected to a power source, only the firstactive electrical heating element 716 is powered. However, if the 240Vpower connector 704 is connected to a power source, both the firstactive electrical heating element 716, and the second active electricalheating element 718 are powered. In this example, the first activeelectrical heating element 716 is powered by the 240V connector throughthe power connection 714.

FIG. 8 illustrates another embodiment of a modular heated cover 800. Inone embodiment, the thermal cover 800 includes the multilayered cover200 comprising a single outer layer 307. However, this alternativeembodiment includes one or more heat spreading layers 804. Thisembodiment additionally includes an electrical connection 802 forconnecting the power plug 212 to an electrical heating element 810.Additionally, an electrical connection 806 may be included to connectmultiple electrical heating elements 810 within a single cover 800.Additionally, the cover 800 may include power connectors 212, 214, powerconnections 216 (not shown in FIG. 8), fasteners 206, folding crease220, and the like.

In one embodiment, the heat spreading layer 804 may comprise a thinlayer of graphite 812, deposited on a structural substrate (not shown).A protective layer (not shown) may be applied to cover the layer ofgraphite 812. Of course layers 302 and 306 may serve, respectively, as astructural substrate and protective layer. The protective layer mayadhere to, or be heat welded to, the substrate. In one embodiment, thegraphite 812 may be deposited as flakes, or a graphite-epoxy compositethat includes graphite flakes, on plastic, vinyl, rubber, metal foil, orthe like. In one embodiment, the graphite element 812 may be integratedwith a thermal insulation layer 304.

Preferably, the graphite 812 draws the heat out of the electricalheating element 810. Advantageously, the graphite 812, substrate, andprotective layer are very thin and light weight.

In one embodiment, the graphite heat spreading layer 804 may be betweenabout 3 and about 20 thousandths of an inch thick. Preferably, thegraphite heat spreading layer 804 is about three feet wide and abouttwenty-three feet long and between about 1 thousandths of an inch thickand about 40 thousandths of an inch thick. In a more preferredembodiment, the graphite heat spreading layer 804 is about fivethousandths of an inch thick. In certain embodiments, each segment ofgraphite heat spreading layer 804 has a surface area between ten squarefeet and 69 square feet. Preferably, two graphite heat spreading layers804 cooperate in a single cover 800 to provide a combined surface areaof between approximately ten square feet and approximately 253 squarefeet.

In certain embodiments, the graphite layer 812 may be between about 1thousandths of an inch thick and about 40 thousandths of an inch thick.This range is preferred because within this thickness range the graphitelayer 812 remains pliable and durable enough to withstand repeatedrolling and unrolling as the cover 800 is unrolled for use and rolled upfor storage.

The small size and thickness of the graphite layer 812 minimizes theweight of the cover 800. The electrical heating element 810 ispreferably pliable such that the cover 800 can be rolled or foldedlengthwise without breaking the electrical path. Advantageously, theelectrical heating element 810 can be manufactured separately andprovided for installation into a cover 800 during manufacturing of thecovers 800.

For example, the electrical heating element 810 may come with electricalconnections 806 and 802 directly from a supplier. The electrical heatingelement 810 may be secured on a bottom facing side of the graphite heatspreading layer 804. Alternatively, the electrical heating element 810may be secured on a top facing side of the graphite heat spreading layer804. The electrical connections 802 may be made to power connections 212and one or more electric power couplings 214. One electrical heatingelement 810 may be connected to a second electrical heating element 810by an electrical connection 806.

The electrical connection 806 serves as an electrical bridge joining thetwo electrical heating elements 810. Preferably, the electricalconnection 806 also bridges a crease 220. The crease 220 facilitatesfolding the cover 800. Preferably, the crease 220 is positioned alongthe horizontal midpoint.

Finally, the remaining layers of thermal insulation 304 and outer cover306 are laid over the top of the graphite heat spreading layer 804 in amanner similar to that illustrated in FIG. 3. Next, the perimeter of thecover 800 may be heat welded for form a water tight envelope for theinternal layers. In addition, residual air between parts of an outerlayer 307 may be extracted from between parts of the outer layer 307such that heat produced by the cover 800 is more readily conductedtoward the bottom cover 306.

It should be noted that in certain embodiments the thermal insulation304 is a layer separate from the cover 800 and is added by a user duringuse of the cover 800. In one embodiment, a user lays insulation materialsuch as straw, regular passive concrete blankets, or the like overembodiments of the cover 800 that do not include an internal thermalinsulation layer 304.

In one embodiment, the electrical heating element 810 is laid out on thegraphite heat spreading layer 804 according to a predetermined pattern814. Those of skill in the art will recognize that a variety of patterns814 may be used. Preferably, the pattern 814 is a zigzag pattern thatmaintains an electrical path and separates lengths 816 of the electricalheating element 810 by a predefined distance 818. Preferably, thedistance 818 is selected such that a maximum amount of the resistanceheat produced by a length 816 is conducted away from the length by thesubstrate, thermal insulation layer 304 and the like. In addition, thedistance 818 is selected such that heat conducted from one length doesnot impede conducting of heat from a parallel length. In addition, thedistance 818 is not so large that cool or cold spots are created. In analternative embodiment, the lengths 816 run lengthwise with respect tothe graphite heat spreading layer 804 as opposed to width-wise asillustrated in FIG. 8. Lengthwise lengths 816 may be organized in apattern similar to that illustrated in FIGS. 2 and 7.

Preferably, the distance 818 is between about 10 inches and about twentyinches wide. Advantageously, this distance range 818 provides for even,consistent heat dissipation across the surface of the cover 800. Thesmaller the distance 818, the lower the possibility of cold spots in thecover 800. By minimizing cold spots, a consistent and even curing ofconcrete or thawing of ground can be accomplished.

The material for the resistive element 208 and/or electrical heatingelement 810 may be conventional materials such as copper, iron, and thelike which have a positive temperature coefficient of resistance.Preferably, the resistive element 208 comprises a material having anegative temperature coefficient of resistance such as graphite,germanium, silicon, and the like. In rush current may be drawn when acover 800 is initially connected to a power source 100 or when a secondcover 800 is coupled to a first cover 800 connected to the power source100. In embodiments in which the resistive element 208 and/or electricalheating element 810 use graphite, the in rush current is substantiallyminimized. Thus, the circuit may be designed to include up to themaximum current draw allowed by the circuit breaker.

In the embodiment illustrated in FIG. 8, the electrical heating element810 and graphite heat spreading layer 804 cooperate to providesufficient heat energy to maintain a temperature between 50 degreesFahrenheit, and 90 degrees Fahrenheit beneath the cover, in freezingambient conditions. Additionally, using such a configuration, it ispossible to connect up to three modular thermal covers on a single 120Volt power source protected by a single 20 Amp circuit. Thus, consistentheat may be provided for between about 300 to about 1000 square feet ofsurface on a single 20 Amp power source.

As indicated in the background above, the modular heated cover 200provides a solution to the problem of accumulated snow, ice, and frostor frozen work surfaces in various construction, residential,industrial, manufacturing, maintenance, agriculture, and service fields.

FIG. 9 is a schematic cross-sectional diagram illustrating oneconfiguration for grounding a modular heated cover. In the depictedembodiment, the multilayer modular heated cover 300 comprises a firstouter layer 302 and a second outer layer 306. As described above, incertain embodiments the first outer layer 302 and second outer layer 306comprise a single outer layer 307. The multilayer modular heated cover300 further comprises the thermal insulation layer 304 which providesthermal insulation to retain heat, as described above. The multilayermodular heated cover 300 additionally comprises a resistive element 208a-b, an electrically insulating element 804, ground coupling 836 a-b,and heat-spreading element 210.

As described above, the resistive element 208 a-b may comprise anymaterial capable of conducting electricity and converting the electricalenergy into heat energy. In a preferred embodiment, the heat isgenerated due to the resistance of the resistive element 208 a-b to theflow of electrons, as is well-known by those of skill in the art.

The multilayer modular heated cover 300 further comprises anelectrically insulating element 804. Electrically insulating element 804is an element that ensures that the current flow through the resistiveelement 208 a-b is isolated from the heat-spreading element 210 which,in the depicted embodiment, is an electrical conductor. Those of skillin the art will recognize that, while the depicted embodiment showselectrically insulating element 804 as a layer, a layer is simply one ofmany possible configurations. For example, the electrically insulatingelement 804 may be isolated to areas directly below the resistiveelement 208 a-b and above the heat-spreading element 210. In otherembodiments, the electrically insulating element 804 is part of amulti-layered electrical heating element such as a heat tape. Examplesof materials suitable for use as an insulating element 804 includeplastic, ceramic, polyethylene, silicon dioxide, Teflon, fish paper, andBiaxially-oriented polyethylene terephthalate (boPET). However, othermaterials known to those of skill in the art may be appropriate for useas an electrical insulator and may be used without departing from theessence of the present invention.

In one embodiment, an appropriate insulating element 804 forms a thinplastic layer on both sides of the heat-spreading element 210. Theinsulating element 804 may additionally provide structure to theheat-spreading material used in the heat spreading element 210. Forexample, the insulating element 804 may be polyethylene terephthalate(PET) in the form of a thin plastic layer applied to both sides of aheat-spreading element 210 comprising graphite. Those of skill in theart will appreciate that such a configuration may result in theinsulating element 804 lending additional durability to theheat-spreading element 210 in addition to providing electricalinsulation.

As a result of the electrically insulating element 804, the resistiveelement 208 a-b is not in electric communication with the heat-spreadingelement 210. Those of skill in the art will recognize that the phrase‘not in electric communication’ indicates that current does not flowwith minimal impedance from one specified element to another, and is notmeant to indicate that the elements are in complete electrical isolationfrom one another. For example, a current through the resistive element208 a-b may induce minor currents in the heat-spreading element 210without being considered ‘in electric communication’ for purposes of thepresent invention.

In a preferred embodiment illustrated in FIG. 9, no additional layer isadded to the cover 300 to facilitate grounding. As a result, the safetyof the cover 300 is increased by providing grounding without acorresponding increase in cost or a corresponding decrease in theeffectiveness of the cover due to greater weight and/or loss offlexibility. Advantageously, grounding is provided by using an existingcomponent for two purposes. Specifically, the heat-spreading element 210serves a thermal dissipation purpose as well as a ground purpose for thewhole cover 300.

The multilayer modular heated cover 300 further comprises groundcouplings 836 a-b. The ground couplings 836 a-b are attached to theelectrically conductive heat-spreading element 210. In one embodiment,the ground couplings 836 a-b are electrically connected to theheat-spreading element 210 in the plane of the heat-spreading element210. Those of skill in the art will recognize that, in many embodiments,such as those in which graphite is used as the material for theheat-spreading element 210, the electrical resistivity of the materialis less within the plane of the layer 210 and greater through thethickness of the layer. For example, the electrical resistivity alongthe plane may be on the order of milli-ohms (μΩ) whereas the electricalresistivity through the thickness is on the order of micro-ohms (mΩ). Assuch, in certain embodiments it is advantageous for the ground couplings836 a-b to be connected in the plane of the heat-spreading element 210.

In one embodiment, the ground couplings 836 a-b comprise planarrectangular metal connection blades that would normally be used as thehot and/or neutral connection blades of a power coupling such asreceiving power coupling 810 which connects to a power source. Those ofskill in the art will recognize that a standard power coupling (whethera receiving power coupling 810 or a female power coupling 830) typicallyincludes a wire, such as ground wire 826, that is intended to beconnected to the device meant to be powered by the power coupling.However, an additional piece such as a ground coupling 836 a-b is neededto secure the wire to the appropriate connection point. In oneembodiment, a blade, as described above, is used as the ground couplings836 a-b in order to make the connection.

Where a blade is used as a ground coupling 836 a-b, the blade isinserted such that it makes and maintains an electrical connection withthe heat-spreading element 210. In certain embodiments, this entailsinserting the blade through an opening in the outer layer 302/307 andthrough the thermal insulating element 304. The blade is furtherconfigured such that it does not make contact with the resistive element208 a-b. In one embodiment, the blade further comprises barbs configuredto cut into the heat-spreading element 210 and engage the heat-spreadingelement 210 such that the blade does not come loose. In alternativeembodiments, the blade may be connected to the heat-spreading element210 with an adhesive that does not electrically insulate theheat-spreading element 210 from the blade. In addition, the plane of theblade may be placed parallel to the plane of the heat-spreading element210 such that a maximum amount of the surface area of the blade is indirect contact with the heat-spreading element 210. Those of skill inthe art will recognize that such a configuration increases the contactarea between the two surfaces and results in a better electrical andphysical connection. Furthermore, such a configuration leverages thelower in-plane resistivity of the heat-spreading element 210.

Other embodiments may be implemented where crimp-on or other connectorsmay be used. For example, in one embodiment AMP/TYCO part number 52195available from Tyco Electronics of Berwyn, Pa. includes barbs that canpierce the heat-spreading element to make electrical contact with theheat-spreading element 210 to accomplish appropriate grounding.

Additionally, foil tape can be applied around the area where a groundingcoupling 836 is used to provide for rigidity or additional strength.This may be particularly useful when a slit is formed in theheat-spreading element 210 to allow a crimp coupling, such as the 52195to be attached to the heat-spreading element 210.

Notably, heated covers can be daisy chained such that power can beprovided from one heated cover 300 to another heated cover 300. Forexample, the receiving power coupling 830 of a first heated cover 300can be connected to a female electric power coupling 810 of a secondheated cover 300 to obtain power for heating the second heated cover300. In accordance with these principles, the ground path between theheated covers 300 may be through the heat-spreading element 210. Inparticular, as illustrated at 836(b), a ground connection may besupplied to a second heated cover by connecting to the heat-spreadingelement 210.

A pliable heating element is an apparatus for heating by convertingelectrical energy to heat energy. The pliable heating element is one ofthe components of a grounded modular heated cover. As discussed above,the combination of the resistive element 208 a-b, heat spreading element210, and electrically insulating element 804 as depicted in FIG. 9 mayconstitute elements of a pliable electrical heating element.

In the depicted embodiment, the multilayer modular heated cover 300further comprises a receiving power coupling 810 and a female electricpower coupling 830. Examples of receiving power coupling 810 include120V plug connectors 702 and 240V power connector 704. The receivingpower coupling 810 is configured to be connected to a power source(whether 120V or 240V) in order to provide the electrical energynecessary to power the resistive element 208 a-b. As taught above, thereceiving power coupling 810 may be connected to the female electricpower coupling 830 of a different grounded modular heated cover suchthat the second cover draws power through the first heated coversufficient to power both blankets. Such a configuration is illustratedand discussed further in FIG. 11.

The receiving power coupling 810 further comprises a hot prong 812, aneutral prong 814, and a grounding prong 816. As known by those of skillin the art, in a standard North American power source (such as wallsocket 1102 shown in FIG. 11), the left slot is neutral, the right ishot, and the bottom is ground. The prongs 812, 814, and 816 areconfigured to be coupled with the associated hot, neutral, and ground ofa standard power source socket. However, configurations of the positionof the hot, neutral, and grounding connections differ around the world.In addition, the shape of the prongs on a receiving power coupling 810and the couplers on a female power coupling 830 may also vary based onthe standards of a particular geographical region. There mayadditionally be changes in the voltages, frequencies, or other powercharacteristics of a power supply in different regions. However, suchvariations are well known to those in the art. The present invention maybe implemented with a variety of possible configurations wherein thegrounded modular heated cover is tailored to a different region withdifferent electrical and power standards without departing from theinvention.

The hot prong 812 and neutral prong 814 of the receiving power coupling810 are connected to the resistive element 208 a-b circuit such that theresistive element 208 a-b is able to utilize the power made available bya power source to which the receiving power coupling 810 is connected.Methods for providing such a connection are well known to those of skillin the art. In the depicted embodiment, the hot prong 812 is connectedto the resistive element 208 a-b through a hot wire 822 and the neutralprong 814 is connected to the resistive element 208 a-b through aneutral wire 824.

In contrast, the grounding prong 816 is connected by the ground wire 826to the ground couplings 836 a-b. In a preferred embodiment, thegrounding prong 816 and the associated ground couplings 836 a-b andheat-spreading element 210 do not carry current from the power sourceduring normal operation of the resistive element 208 a-b circuit. Thoseof skill in the art will further appreciate that a power sourcetypically provides a grounding system sufficient to act as a properground for a device properly connected through a grounding pin 816.Instead, the grounding prong 816 and the associated ground couplings 836a-b and heat-spreading element 210 serve a safety function.

The multilayer modular heated cover 300 further comprises a femaleelectric power coupling 830. The female electric power coupling 830further comprises a neutral coupler 832, a hot coupler 834, and a groundcoupler 856. The female electric power coupling 830 is configured toreceive a male electric power coupling such as receiving power coupling810. As such, the female electric power coupling 830 may be used toconnect one grounded modular heated cover to a second grounded modularheated cover by connecting a receiving power coupling 810 of the firstcover to the female electric power coupling 830 of the second cover.

Similar to the receiving power coupling 810, the hot coupler 834 andneutral coupler 832 are connected respectively by hot wire 842 andneutral wire 832 to the resistive element 208 a-b such that a coverconnected by the female electric power coupling 830 becomes part of thecircuit. Those of skill in the art will appreciate that a person couldconnect the receiving power coupling of other apparatus to the femaleelectric power coupling 830 such that the apparatus would constitutepart of the electric circuit.

FIG. 10 is a schematic block diagram illustrating an alternativeconfiguration comprising a grounding layer for grounding a modular heatcover. In addition to items depicted in FIG. 9, the multilayer modularheated cover 300 further comprises a grounding layer 1008, groundinglayer coupling 1010, grounding connection 1006, hot connection 1002, andneutral connection 1004. While the depicted embodiment does include anadditional grounding layer 1008, increasing the weight and cost ofmanufacture, the inclusion of the additional grounding layer 1008 mayprovide an added level of safety by positioning the current-carryingelement (such as resistive element 208) between the grounding layer 1008and the heat-spreading element 210. In such an embodiment, greatersafety results by grounding both the grounding layer 1008 and theheat-spreading element 210 to a common ground. Grounding only thegrounding layer 1008 does not provide an additional safety benefit overthe embodiment described in FIG. 9 and carries the costs of increasedweight and increase manufacturing costs.

Grounding layer 1008 comprises a layer of electrically-conductivematerial with sufficiently low resistance to provide a connection toground through the grounding layer coupling 1010, grounding connection1006, and, ultimately, the ground of the power source. In oneembodiment, the grounding layer 1008 may be foil. Alternatively, thegrounding layer 1006 may be a layer of graphite or other carbon-basedmaterial. In one embodiment, the grounding layer 1008 is disposed in themultilayer modular heated cover 300 such that the resistive element 208a-b is between the grounding layer 1008 and the electrically-conductiveheat spreading layer 210.

In such an embodiment, the heat spreading layer 210 is connected toground in a fashion similar to that depicted and explained in FIG. 9.While the embodiment depicted in FIG. 10 illustrates the heat-spreadinglayer 836 and grounding layer 1008 connected to ground through a commongrounding connection 1006, those of skill in the art will appreciatethat the two may share a different grounding connection 1006 through themultilayer modular heated cover 300 and come to a common grounding prong816 such that the grounding layer 1008 and heat-spreading element 210share a common ground. Alternatively, either the grounding layer 1008 orthe heat-spreading element 210 may be grounded to a power source groundlead.

Those of skill in the art will appreciate that such a configuration mayoffer additional safety benefits by increasing the likelihood that,should a problem arise which may result in a person coming into contactwith a current-carrying element of the multilayer modular heated cover300 (such as the resistive element 208 a-b), the current-carryingelements are ‘sandwiched’ between the grounding layer 1008 andheat-spreading element 210. As a result, it is more likely that thecurrent-carrying elements will come into contact with ground before aconnection is made with a person, thus avoiding a potentially hazardoussituation.

In one embodiment, the grounding layer 1008 is situated such that thethermal insulating element 304 is between the grounding layer 1008 andthe resistive element 208 a-b. Such a configuration reduces the heatabsorption by the grounding layer 1008, increasing the heat transferredto the heat-spreading element 210.

FIG. 11 is a schematic block diagram illustrating an exemplaryembodiment of a grounding connection for a system comprising a pluralityof modular heated covers. The system comprises grounded modular heatedcovers 1120, 1130, 1140, and 1150. The system further comprises a powersource 1102. In one embodiment, the depicted power source 1102 is astandard 120V wall socket. The power source 1102 further comprises a hotslot 1106, neutral slot 1104, and a grounding slot 1108. As depicted,the grounding slot 1108 constitutes a connection to the ground (such asan earth electrode) of the power source.

FIG. 11 further depicts a hot rail 1162 and a neutral rail 1160. As isknown to those in the art, the rails 1162 and 1160 are the electricalconnections from the power source 1102 to the grounded modular heatercovers 1120, 1130, 1140, 1150. In one embodiment, the connection is madeas depicted and described in connection to FIGS. 6-9. For ease ofexplanation, the connections are modeled as rails 1160 and 1162, andeach of the covers 1120, 1130, 1140, and 1150 is modeled as a resistor.As known to those of skill in the art, the depicted embodimentrepresents a parallel circuit configuration.

FIG. 11 further depicts a ground connection 1164 a-d. As shown anddescribed in FIG. 9, ground connections 1164 a-d may be made by way ofthe female electric power coupling 830 of a cover and the receivingpower coupling 810 of a second cover. For example, the cover 1150 isattached through the cover 1150's receiving power coupling 810 to thefemale electric power coupling 830 of the cover 1140. This connectionputs the cover 1150 electrically in parallel with the cover 1140, asdepicted. Those of skill in the art will recognize that this depictionis representative of one possible configuration, and is not a limitationon how the connections may be made. For example, the grounded modularheated covers may be wired such that a connection of multiple coversforms a series electrical connection as opposed to a parallelconnection.

In addition, the grounding prong 816 of the cover 1150's receiving powercoupling 810 is electrically connected to the heat-spreading element 210of the cover 1150 by the ground coupling 836. The grounding coupler 856of the cover 1140's female electric power coupling 830 is electricallyconnected to the heat-spreading element 210 of the second cover 1140.The electrical connection between the two heat-spreading elements 210 isdepicted by ground connection 1164 a. A connection is similarly madebetween all of the system components, as depicted by ground connections1164 b (linking 1140 and 1130), 1164 c (linking 1130 and 1120) and 1164d (linking 1120 to the grounding slot 1108 of the power source 1102. Asa result, the ground connections form a series electrical ‘chain’ fromthe furthest element (1150) to the source (1102).

As appreciated by those of skill in the art, the ground connection 1164a is not a normal part of the operation of the circuit. As such, absenta failure within one of the modular covers 1150, 1140, 1130, of 1120,the grounding connections 1164 a-d do not play an active role. However,if a fault occurs in any of the covers 1120, 1130, 1140, or 1150 suchthat a connection is established between, for example, the hot rail 1162and the heat-spreading element 210 of any cover, the groundingconnections 1164 a-d become an active part of the circuit, drawing thecurrent from the hot rail 1102 to the grounding slot 1108. Such aconfiguration provides an added measure of safety as it ensures that thecurrent follows the low-resistance path to ground (grounding path 1164a-d) instead of taking a path through an individual using the covers.Further, it is common for power sources 1102 to comprise a breaker orother sensor such that the return current flow through the groundingpath 1164 a-d triggers safety systems that will turn off the powersupplied through the hot rail 1102.

For example, if a fault occurs in cover 1140 such that a connection isestablished from the hot rail 1102 to the heat-spreading element 210 ofcover 1140, the grounding connections 1164 b-d provide a path for thecurrent such that it flows: from the hot rail 102 through the groundingconnection 1164 b to the heat-spreading element 210 of cover 1130, thento the heat-spreading element 210 of cover 1120 through groundingconnection 164 c, and finally to the power source ground (grounding slot1108) through the grounding connection 1164 d.

FIG. 12 is a schematic block diagram illustrating an alternativeconfiguration comprising a grounding sheath 1204 for grounding a modularheat cover. In the depicted embodiment, the resistive element 208 isencompassed by a grounding sheath 1204. The grounding sheath 1204 iselectrically connected to the grounding prong 816 of a receiving powercoupling 810. Similarly, the grounding sheath 1204 may be connected tothe grounding coupler 856 of a related female electric power coupling830. Similar to that shown and discussed in FIG. 9, by making the aboveelectrical connections the grounding sheath 1204 is in electricalcommunication with the ground of the driving power source. In oneembodiment, the sheath 1204 may be made of electrically-conductivematerial such as copper or graphite. In one embodiment, the sheath maybe made of a material such as carbon fiber which has high electricalconductivity and low thermal conductivity such that the sheath 1204 actsas an adequate ground but absorbs minimal heat from the resistiveelement 208. Alternatively, the sheath 1204 may be made of a materialwith both high electrical conductivity and high thermal conductivitysuch as copper, such that the sheath 1204 absorbs the heat generated bythe resistive element 208 and acts as if it were the source of the heat.Thus, the heat would transfer from the sheath 1204 to the heat-spreadingelement 210. In a preferred embodiment, the sheath 1204 is electricallyinsulated from the heat-spreading element 210 if the heat-spreadingelement 210 is an electrical conductor.

The embodiment in FIG. 12 further comprises an electrically insulatingsheath 1202. The electrically insulating sheath 1202 ensures that thecurrent in the resistive element 208 does not flow through the groundingsheath 1204. Examples of materials suitable for use as an electricallyinsulating sheath 1202 include polyethylene, silicon dioxide, Teflon,fish paper, and Biaxially-oriented polyethylene terephthalate (boPET).However, other materials known to those of skill in the art may beappropriate for use as an electrical insulator and may be used withoutdeparting from the essence of the present invention.

The grounding sheath 1204 may be formed as a single unitary piececontaining the resistive element 208. The grounding sheath 1204 may alsobe a made of a number of pieces of appropriate material configured toencompass the resistive element 208 as shown in FIG. 12. For example,the grounding sheath 1204 may be a sheet of material folded around theresistive element 208 to form the depicted encompassing enclosure.Alternatively, the grounding sheath 1204 may be made of material braidedtogether to form the enclosure depicted in FIG. 12. The insulatingsheath 1202 may be similarly formed.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A heating unit comprising: a first outer layer; a second outer layer;a heating element disposed between the first and second outer layers,the heating element comprising: a heat generating element for generatingheat energy; and a carbon-based heat spreading element positionedadjacent the heat generating element, the heat spreading elementconfigured to substantially uniformly distribute the heat energy; and athermal insulation layer positioned between the heating element and thefirst outer layer to direct the heat energy toward the second outerlayer.
 2. The heating unit of claim 1, wherein the first or second outerlayer comprises burlap, canvas, cotton, nylon, or vinyl.
 3. The heatingunit of claim 1, wherein the thermal insulation layer comprisespolystyrene, cotton, poly-tetra-fluoro-ethylene, or fiberglass.
 4. Theheating unit of claim 1, wherein the carbon-based heat spreading elementcomprises graphite.
 5. The heating unit of claim 1, wherein the firstand second outer layers are sealed together to form a water resistantenvelope around the thermal insulation layer and electrical heatingelement.
 6. The heating unit of claim 1, wherein the heat generatingelement comprises a resistive element adapted to convert electricalenergy to heat energy.
 7. The heating unit of claim 6, wherein the heatgenerating element is coupled to a receiving power connector, thereceiving power connector configured to couple to an electrical powersource to supply electrical energy to the heat generating element. 8.The heating unit of claim 1, wherein the heat generating element isthermally coupled to the heat spreading element.
 9. The heating unit ofclaim 1, wherein the heat generating element is positioned between theheat spreading element and the thermal insulation layer.
 10. The heatingunit of claim 1, wherein the heating unit is adapted to substantiallyuniformly heat a surface adjacent the second outer layer.
 11. A heatingunit comprising: a heat generating element coupleable to an electricalpower source to supply electrical energy to the heat generating element,the heat generating element being adapted to convert the electricalenergy to heat energy; a carbon-based heat spreading element, theelectrical heat generating element being attached to a first side of theheat spreading element, the heat spreading element being configured tosubstantially uniformly distribute the heat energy over a surfaceadjacent thereto; and a thermal insulation layer positioned adjacent theelectrical heat generating element and the first side of the heatspreading element to direct the heat energy toward a second side of theheat spreading element.
 12. The heating unit of claim 11, furthercomprising first and second cover layers to substantially enclose theheat generating element, the heat spreading element, and the thermalinsulation layer.
 13. The heating unit of claim 12, wherein the firstcover layer is adapted to absorb heat energy from an externalenvironment.
 14. The heating unit of claim 12, wherein the second coverlayer is adapted to convey heat energy to an external environment. 15.The heating unit of claim 12, wherein the first and second cover layersare formed of a pliable material.
 16. The heating unit of claim 11,wherein the heat generating element and the heat spreading element areformed of pliable materials.
 17. The heating unit of claim 11, whereinthe heating unit is adapted to transfer heat energy to a surfaceadjacent the second side of the heat spreading element.
 18. The heatingunit of claim 17, wherein the heating unit is adapted to heat andmaintain the surface to temperatures between 50° F. and 90° F.
 19. Theheating unit of claim 18, further comprising a thermostat to enableselective adjustment of the temperature.
 20. The heating unit of claim11, wherein the heat spreading element comprises graphite.
 21. A heatingunit for uniformly transferring heat energy to a surface or object, theheating unit comprising: a first cover layer and a second cover layerthat are attached together to form a substantially enclosed interiorportion therebetween; an electrical heating element enclosed within theinterior portion formed by the first and second cover layers, theelectrical heating element comprising: a heat generating element adaptedto convert electrical energy to heat energy; and a planar graphite heatspreading element, the electrical heat generating element beingthermally coupled to the heat spreading element to facilitate transferof the heat energy from the heat generating element to the heatspreading element, the heat spreading element being configured tosubstantially uniformly distribute the heat energy to a surface orobject adjacent the heating unit; and a thermal insulation layerenclosed within the interior portion formed by the first and secondcover layers, the thermal insulation layer being positioned between thefirst cover layer and the electrical heating element, the thermalinsulation layer being adapted to direct the heat energy toward thesecond cover layer; one or more fasteners disposed in the first orsecond cover layers to enable the heating unit to be secured on, around,or to a surface or object; and a receiving power connector electricallyconnected to the heat generating element, the receiving power connectorconfigured to couple to an electrical power source to supply electricalenergy to the heat generating element.
 22. The heating unit of claim 21,further comprising an outgoing electrical connector electrically coupledto the receiving power connector, the outgoing electrical connectorbeing configured to couple to receiving power connectors of otherheating units.
 23. The heating unit of claim 21, wherein the heatingunit is adapted to be rolled or folded.
 24. A heating unit for uniformlytransferring heat energy to a surface or object, the heating unitcomprising: a first cover layer and a second cover layer, wherein edgesof the first cover layer are attached to edges of the second cover layerto form a substantially enclosed interior portion between the first andsecond cover layers; an electrical heating element enclosed within theinterior portion formed by the first and second cover layers, theelectrical heating element comprising: a heat generating element adaptedto convert electrical energy to heat energy; and a planar graphite heatspreading element, the electrical heat generating element being attachedto a first side of the heat spreading element and thermally coupled tothe heat spreading element to facilitate transfer of the heat energyfrom the heat generating element to the heat spreading element, the heatspreading element being configured to substantially uniformly distributethe heat energy to a surface or object adjacent the second cover layer;and a thermal insulation layer enclosed within the interior portionformed by the first and second cover layers, the thermal insulationlayer being positioned between the first cover layer and the electricalheat generating element and the first side of the heat spreadingelement, the thermal insulation layer being adapted to direct the heatenergy toward the second cover layer; one or more insulation flapsdisposed about the periphery of the heating unit, the insulation flapsbeing adapted to maintain the heat energy between the heating unit andthe surface or object being heated; one or more fasteners disposed inthe first cover layer, the second cover layer, or the one or moreinsulation flaps to enable the heating unit to be secured on, around, orto a surface or object; a receiving power connector electricallyconnected to the heat generating element, the receiving power connectorconfigured to couple to an electrical power source to supply electricalenergy to the heat generating element; and an outgoing electricalconnector electrically coupled to the receiving power connector, theoutgoing electrical connector being configured to couple to receivingpower connectors of other heating units.
 25. The heating unit of claim24, wherein the one or more fasteners comprise grommets.
 26. The heatingunit of claim 24, wherein the one or more fasteners comprise permanentattachment of one portion of the heating unit to an opposing portion ofthe heating unit such that the heating unit permanently maintains asubstantially wrapped shape.
 27. The heating unit of claim 24, whereinthe one or more fasteners comprise snaps with mating portions of thesnaps disposed on opposing portions of the heating unit.
 28. The heatingunit of claim 24, wherein the one or more insulation flaps are formed bythe first and second cover layers.